Hereinafter in this application, use is made of an earth frame of reference which comprises:
An axis X0 which corresponds to a horizontal axis oriented northwards.
An axis Y0 which is horizontal, perpendicular to the axis X0 and oriented eastwards.
An axis Z0 which is perpendicular to the axes X0 and Y0 and oriented downwards.
The axes X0 and Y0 define a horizontal plane and the axis Z0 corresponds to the vertical direction.
To define the motions of an aeroplane, an aeroplane frame of reference is associated therewith, comprising:                An axis X1 which extends from the rear tip to the front tip of the aeroplane and which is linked to the aeroplane, also called the aeroplane longitudinal axis X1,        An axis Y1 which is perpendicular to the axis X1 and which is oriented in the direction of the aerofoil of the aeroplane, also called the aeroplane transverse axis Y1,        An axis Z1 which is perpendicular to the axes X1 and Y1 and oriented downwards.        
With respect to the earth frame of reference, when the aeroplane pivots about the axis Y1 (pitch), the angle θ between the aeroplane longitudinal axis X1 and the horizontal plane is called the trim. When the aeroplane pivots about the axis X1 (roll), the angle Φ between the aeroplane transverse axis Y1 and the horizontal plane is called the bank.
The attitude of the aeroplane corresponds to the position of the aeroplane with respect to the horizontal plane and is characterized by the trim and the bank of the aeroplane.
The cockpit of an aircraft comprises an artificial horizon which indicates the attitude of the aeroplane. The artificial horizon is positioned in front of the pilot.
According to one embodiment, the artificial horizon takes the form of a screen on which is displayed information relating to the attitude of the aeroplane originating from a gyroscopic system and/or from an inertial platform. The screen comprises a blue upper part symbolizing the sky, a brownish lower part symbolizing the earth and an artificial horizon line separating the upper and lower parts. A schematic representation of the aeroplane is positioned with respect to this artificial horizon line as a function of the attitude of the aeroplane.
Despite this presentation of the information, the artificial horizon is perceived by pilots as an artificial aid, possibly prone to faults. In situations of stress, for example during the triggering of alarms, pilots may have a tendency to accord greater confidence, in respect of positioning in space, to their sensations rather than to the information transmitted to them by the aeroplane's instruments. It is nevertheless substantiated that, usually, the information given by the aeroplane's instruments is more reliable than pilots' sensations. Indeed, the absence of any exterior visual frame, the flight conditions and stress may impair the pilot's sensations and give rise to spatial disorientation. The loss of confidence, by the pilot, in the information given by the artificial horizon can then lead to situations of risk.